Paleo-Glacier Equilibrium Line Altitudes around Nevado de Chañi, Arid Subtropical Andes

JOSHUA CHARLTON; SUMMER RUPPER; MATEO MARTINI; KAPLAN, MICHAEL; SIMON BREWER; SCHAEFER, JOERG M.

Congreso; American Geophysical Union Fall Meeting; 2022

Glaciationalong the high Andes exhibits remarkable geographic variation. The aridsubtropical region is particularly unique because it hosts peaks exceeding 5000m asl that are not presently glaciated. Several peaks intersect the annual 0˚Cisotherm, but the region is too dry to support glaciers. Nevertheless, glacialvalleys and moraines throughout the region document extensive glaciations inthe past, which were driven by greater snowfall accumulation, associatedreductions in net shortwave radiation, and reduced temperatures. However, thevariability and magnitude of glacial expansion across the region is stilllargely unresolved. Here, we use a new model to calculate the steady-state equilibriumline altitude (ELA) of paleo-glaciers in the arid subtropical Andes. Our modelis based on mass continuity equations and thus bypasses the subjective processof selecting or tuning empirical coefficients, which is an important advantagein regions without modern glaciers for reference. Another novel advantage isthat it leverages Monte Carlo sampling to inform the ELA estimates with uncertaintiesin modeled paleo-glacier geometry. The result is a first-order distribution ofplausible ELA values for each paleo-glacier. The model requires only a DEM ofthe valley topography and a shapefile of the valley outline as inputs, and fromthere automatically generates the central flowline, glacier thickness and widthat discrete points along the flowline, and robust uncertainty bounds for theglacier geometry. We focus our study on the Nevado de Chañi massif inCordillera Oriental, northwest Argentina. Glacial valleys are far moreextensive on the east side of the massif than the west side, making Nevado deChañi an ideal natural laboratory for testing how interactions between climateand topography locally control the extent of glaciation. Beryllium-10 ages fromprior work around the massif indicate moraine formation during Marine IsotopeStage 3, the global Last Glacial Maximum, Heinrich Stadial 1, and the YoungerDryas. With chronology in hand, we apply the ELA model to glacial valleys acrossthe massif to quantify the time-evolution of glaciation through the latePleistocene. Finally, we use statistical relationships to quantify theinfluence of topographic parameters on ELA variation between valleys.